Field of the Invention
The invention relates to extruded aluminum-copper-lithium alloy products, and more particularly to such products, their manufacturing processes and use, notably designed for aeronautical and aerospace engineering.
Description of Related Art
Extruded products made of aluminum alloy are developed to produce high strength parts designed for the aeronautical and aerospace industry in particular.
Extruded products made of aluminum alloy are used in the aeronautic industry for numerous applications, such as fuselage stringers and stiffeners, circumferential frames, wing stiffeners, floor beams or profiles and seat tracks.
The progressive incorporation of more composite materials in aeronautical structures has modified the requirements regarding extruded products incorporated in aircraft, notably for structural elements such as floor beams. It was found that the energy absorption during an impact, or more particularly in a crash, is now a major criterion in the selection of this product. Other important properties are the highest mechanical characteristics possible, in order to reduce structural weights and corrosion resistance.
A quantity such as the specific energy absorption capacity may be used to characterize energy absorption during an impact.
The specific energy absorption capacity during an impact may be measured during a crushing test in which the force supplied is measured according to the displacement produced during the crushing. This is the amount of energy expended to crush a unit mass of material in the stable crushing phase. Ductile aluminum alloys have a high capacity to absorb energy upon impact, particularly as they deform plastically. As an initial approximation, the specific energy absorption capacity during an impact of a profile made of aluminum alloy can be associated with the curve obtained during a tensile test of the material concerned, particularly in the area below the force-deformation curve. It can therefore be evaluated by the product Rm×E % or Rp0.2×E % in the L-direction and in the LT-direction.
Al—Cu—Li alloys are known.
U.S. Pat. No. 5,032,359 describes a vast family of aluminum-copper-lithium alloys in which the addition of magnesium and silver, in particular between 0.3 and 0.5 percent by weight, makes it possible to increase the mechanical strength.
U.S. Pat. No. 5,455,003 describes a process for manufacturing Al—Cu—Li alloys that have improved mechanical strength and toughness at cryogenic temperature, in particular owing to appropriate strain hardening and aging. This patent particularly recommends the composition, expressed as a percentage by weight, Cu=3.0-4.5, Li=0.7-1.1. Ag=0-0.6, Mg=0.3-0.6 and Zn=0-0.75.
U.S. Pat. No. 7,438,772 describes alloys including, expressed as a percentage by weight, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9 and discourages the use of higher lithium content because of a reduction in the balance between toughness and mechanical strength.
U.S. Pat. No. 7,229,509 describes an alloy including (wt %): (2.5-5.5) Cu, (0.1-2.5) Li, (0.2-1.0) Mg, (0.2-0.8) Ag, (0.2-0.8) Mn, 0.4 max Zr or other grain-refining agents such as Cr, Ti, Hf, Sc, and V.
US patent application 2009/142222 A1 describes alloys including (as a percentage by weight), 3.4 wt % to 4.2 wt % Cu, 0.9 wt % to 1.4 wt % Li, 0.3 wt % to 0.7 wt % Ag, 0.1 wt % to 0.6 wt %, Mg, 0.2 wt % to 0.8 wt % Zn, 0.1 wt % to 0.6 wt % Mn and 0.01 wt % to 0.6 wt % of at least one element for controlling the granular structure. This application also describes a process for manufacturing extruded products.
There exists a need for extruded products made of aluminum-copper-lithium alloy presenting improved properties as compared with those of known products, particularly in terms of energy absorption during an impact, static mechanical strength and corrosion resistance properties, while being of low density. Simultaneously, satisfactory toughness must be maintained for these products.